Conventionally, there is studied a communication method called HSDPA (High Speed Downlink Packet Access) as a high-speed IMT-2000 packet transmission method for the purpose of high-speed downstream peak transmission rate, low transmission delay, and high throughput. There are disclosed transmission methods called AMC (Adaptive Modulation and Coding) as a technique of assisting HSDPA in 3GPP (3rd Generation Partnership Project) TR25.848 “Physical layer aspects of UTRA High Speed Downlink Packet Access, and TR25.858 “HSDPA Physical Layer Aspects”.
In HSDPA, one physical channel is shared and used by plural mobile stations by time sharing. Therefore, a base station determines which mobile station should receive information at one point based on line quality.
The AMC technique is used to properly change a modulation method or an error correction coding rate at high speed according to a variation in line quality.
In the AMC technique, as the line quality becomes better, the higher modulation method is adopted, the error correction coding rate is enhanced, and transmission rate is also enhanced.
In the AMC technique, the base station allocates the modulation method and coding rate (MCS: Modulation and Coding Scheme) to each mobile station based on the line quality.
Specifically, the base station measures the downstream line quality, the base station determines the optimum transmission rate based on the measured line quality, and the base station transmits various pieces of information to the mobile station side at the determined transmission rate.
CQI (Channel Quality Indicator) can be cited as an example of the line quality. CQI is information for notifying the base station in communication of the transmission rate receivable on the mobile station side. CQI is determined based on reception quality on the mobile station side.
A wireless communication system which enables downstream high-speed packet communication will be described with reference to FIG. 1.
The wireless communication system includes a mobile station (1-1 to 1-N: N is an arbitrary integer) and a base station (100-1 to 100-N: N is an arbitrary integer). The base station (100-1 to 100-N) transmits transmission data (packet data) to the mobile station (1-1 to 1-N) located in a cell.
An internal configuration of the mobile stations (1-1 to 1-N) shown in FIG. 1 will be described with reference to FIG. 2.
The mobile stations (1-1 to 1-N) includes an antenna 11, an antenna sharing device 12, a reception unit 13, a reverse diffusion unit 14, a packet data demodulation unit 15, a packet buffer 16, a CPU 17, a packet retransmission request signal generation unit 18, BLER (Block Error Rate) measuring unit 19, CQI (Channel Quality Indicator) generation unit 20, a control channel generation unit 21, a multiplexing unit 22, a modulation unit 23, a diffusion unit 24, and a transmission unit 25.
A series of processing operations in the mobile station (1-1 to 1-N) shown in FIG. 2 will be described.
The mobile station (1-1 to 1-N) receives an RF signal transmitted from the base station (100-1 to 100-N) using the antenna 11, and the mobile station (1-1 to 1-N) outputs the received RF signal to the antenna sharing device 12.
The antenna sharing device 12 outputs the RF signal input from the antenna 11 to the reception unit 13. The reception unit 13 converts the RF signal input from the antenna sharing device 12 into a baseband signal, and the reception unit 13 outputs the converted baseband signal to the reverse diffusion unit 14.
The reverse diffusion unit 14 performs reverse diffusion processing of the baseband signal input from the reception unit 13, and the reverse diffusion unit 14 outputs the reverse diffusion processed data to the packet data demodulation unit 15.
The packet data demodulation unit 15 generates packet data by demodulating the data input from the reverse diffusion unit 14, and the packet data demodulation unit 15 outputs the generated packet data to the packet buffer 16.
The packet buffer 16 tentatively retains the packet data input from the packet data demodulation unit 15, and the packet buffer 16 outputs the tentatively retained packet data to the CPU 17.
The packet data demodulation unit 15 also detects error data based on the packet data, and the packet data demodulation unit 15 outputs packet data identification information for identifying the packet data in which the error data is detected to the packet retransmission request signal generation unit 18.
The packet retransmission request signal generation unit 18 generates packet retransmission request control data based on the packet identification information input from the packet data demodulation unit 15, and the packet retransmission request signal generation unit 18 outputs the generated packet retransmission request control data to the control channel generation unit 21. As used herein, the packet retransmission request control data means control data used to make a packet data retransmission request to the base station (100-1 to 100-N).
The packet data demodulation unit 15 also outputs the error data detected based on the packet data to the BLER measuring unit 19.
The BLER measuring unit 19 measures a BER value based on the error data input from the packet data demodulation unit 15 and an amount of error data, and the BLER measuring unit 19 outputs the measured BER value to the CQI generation unit 20.
The CQI generation unit 20 compares the BER value input from the BLER measuring unit 19 and a predetermined reference value p. When the CQI generation unit 20 determines that the BER value input from the BLER measuring unit 19 is lower than the reference value p (BER value<P), the CQI generation unit 20 sets a CQI value to a level higher than that of the currently-set CQI value, and the CQI generation unit 20 outputs the set CQI value to the control channel generation unit 21. When the CQI generation unit 20 determines that the BER value input from the BLER measuring unit 19 is not lower than the reference value p (BER value≧P), the CQI generation unit 20 sets the CQI value to a level lower than that of the currently-set CQI value, and the CQI generation unit 20 outputs the set CQI value to the control channel generation unit 21.
The control channel generation unit 21 multiplexes the packet retransmission request control data input from the packet retransmission request signal generation unit 18, the CQI value input from the CQI generation unit 20, and other pieces of control data to generate a control channel, and the control channel generation unit 21 outputs the generated control channel to the multiplexing unit 22.
The multiplexing unit 22 multiplexes the control channel input from the control channel generation unit 21 and other channels to generate multiplexed data, and the multiplexing unit 22 outputs the multiplexed data to the modulation unit 23.
The modulation unit 23 generates modulated data by performing modulation processing to the multiplexed data input from the multiplexing unit 22, and the modulation unit 23 outputs the generated modulated data to the diffusion unit 24.
The diffusion unit 24 generates a baseband signal by performing diffusion processing of the modulated data input from the modulation unit 23, and the diffusion unit 24 outputs the generated baseband signal to the transmission unit 25.
The transmission unit 25 generates an RF signal based on the baseband signal input from the diffusion unit 24, and the transmission unit 25 outputs the generated RF signal to the antenna sharing device 12.
The antenna sharing device 12 transmits the RF signal, input from the transmission unit 25, to the base station (100-1 to 100-N) through the antenna 11.
Therefore, the mobile station (1-1 to 1-N) transmits the CQI value set in the CQI generation unit 20 to the side of the base station (100-1 to 100-N), so that the mobile station (1-1 to 1-N) can notify the base station (100-1 to 100-N) of an upper limit of a transmission rate receivable on the side of the mobile station (1-1 to 1-N).
In the mobile station (1-1 to 1-N), when MCS (Modulation and Coding Scheme) approaches a maximum value, huge amounts of downstream data are generated to increase an amount of processing necessary for decode processing and packet processing. Therefore, high processing capability is required for the packet buffer 16 and CPU 17.
Recently communication methods (such as USB, BLUETOOTH, WLAN, and communication between CPUs) except for the wireless communication are mounted on the mobile station (1-1 to 1-N) with an extension of functionality of the mobile station (1-1 to 1-N), and the increase in processing capacity becomes unavoidable in the packet buffer 16 in the future.
Additionally, the increase in processing capacity also becomes unavoidable in the CPU 17 with the progress of the complicated and sophisticated application processing computation.
The state in which various kinds of communication and various applications are competitively operated is also increasing due to multi-task processing and multi-job processing. Therefore, in order to guarantee all the competitive operations, it is necessary that the packet buffer 16 and CPU 17 have extremely high performance.
For example, Patent Document 1 which was filed in advance of the present invention discloses a channel system which includes a common interface used to perform data transfer between an upper hierarchical device and a peripheral control device and a channel control device and a peripheral control device which are connected through the common interface. The channel control device includes a data buffer in which transferred data is tentatively stored, an overrun detection circuit which detects overrun, in which the data transfer cannot be performed when the amount of data stored in the data buffer exceeds storage capacity or when data stored in the data buffer does not exist, a first transfer mode register which determines a data transfer rate, a first transfer mode control circuit which changes a data transfer rate to the data transfer rate determined by the first transfer mode register when the overrun detection circuit detects the overrun, and a first common interface control circuit which controls the common interface to a predetermined transfer rate by a command of the first transfer mode control circuit. The peripheral control device includes a second transfer mode register which determines the data transfer rate, a second transfer mode control circuit which changes a data transfer rate to the data transfer rate determined by the second transfer mode register when the overrun detection circuit detects the overrun, and a second common interface control circuit which controls the common interface to a predetermined transfer rate by a command of the second transfer mode control circuit. The channel system prevents second generation of overrun in a retrial after the overrun is generated.
For example, Patent Document 2 discloses wireless communication system in which a transmission device retransmits plural carrier waves in response to a retransmission request from a reception device. The transmission device transmits the plural carrier waves while transmission data is mapped, and frequencies are changed according to a predetermined frequency hopping pattern in the plural carrier waves. The reception device receives the plural carrier waves. The reception device notifies the transmission device of the interference carrier wave in the received plural carrier waves. The transmission device retransmits transmission data mapped in the interference carrier wave as a priority in order to enhance a data retransmission processing effect to improve reception performance on the reception side.
Patent Document 1: Japanese Patent Publication Laid-Open No. 5-20247
Patent Document 2: Japanese Patent Publication Laid-Open No. 2004-266739